Piping systems and pipelines are subject to defects such as arc burns, corrosion, cracks, dents, fretting, gouges, and grooves that compromise structural integrity. Because of the potential of a defect to cause catastrophic failure, pipeline operators employ various external and internal inspection methods to evaluate pipeline conditions and identify defects. When a defect is identified, various repair methods are employed based upon such factors as defect location, type, and size. Repair methods include grinding, weld deposit, sleeves, clamps, and hot tapping. Preferably, operators would like to make the repair without having to shutdown or reduce the flow of the pipeline.
An advance in sleeve-type repairs has been the use of composite materials. The composite is typically multiple layers of carbon, glass, or aramid fibers bound together by a polymeric matrix consisting of either epoxy, polyurethane, or vinlyester in the form of a patch or wrap. First, the surrounding pipeline surfaces are prepared to receive the composite wrap and filler by grit-blasting or an equivalent process. In a typical repair, putty filler is used to fill any voids in the pipeline created by the defect and to taper uneven welds or misaligned pipes. The surface is then prepared with low viscosity polymeric primer to ensure bonding and load transfer between the repair and the substrate. The structural reinforcing fibers, or fabric, are then saturated with a liquid polymer and the wet fibers are wrapped around the outer pipeline surface. The wrap is then allowed to cure at ambient temperature and atmospheric pressure.
Composite wrap repairs can be difficult and labor intensive due in part to the handling of the wet fibers and the time-sensitive nature of the liquid polymer. As the polymer set-up time or pot life expires, the liquid polymer becomes more viscous and difficult to mold and shape. Unlike cure time, which may be a day or several days, the pot life of many liquid polymers is only a few minutes.
Other types of composite wrap systems include pre-impregnated layers and pre-cured coils. A pre-impregnated system is one that has a polymer applied onto the fibers at the factory; however, the polymer is not fully cured at this stage. Reaction of the polymer is achieved by the addition of heat or a chemical (including water) to the pre-impregnated fiber. This means that a liquid polymer is applied to dry fibers at a factory and the reaction is suspended until heat or some type of chemical is added to the system once it is applied to the pipeline.
In a pre-cured coil, the repair system is shipped from the factory with the polymer completely reacted onto the fibers. Each layer of the repair system is therefore pre-cured and is pre-formed to the pipeline outer diameter. In the field, this pre-cured coil is pulled around the pipeline and an adhesive is applied to each layer to bond the coil together.
Externally applied repair systems present safety concerns. Pipeline operators do not like to work on a pipe directly over a defect under pressure. Yet, in all composite over-wrap systems, the external surface of the pipeline directly above the defect must be cleaned in order for the composite to bond at the defect. If the external pipe was grit-blasted or mechanically cleaned too severely, the cleaning could thin the wall to a point of failure.
To provide for improved safety, a number of patents disclose pressure isolating the repair area. For example, U.S. Pat. No. 6,752,175, issued to Willschuetz et al., discloses a wirelessly controlled pig that engages a sealing element to pressure isolate a section of pipeline in order to perform work, such as hot tapping, from the outside of the pipeline. No provision, however, is provided by Willschuetz et al. for internal pipeline repair with composites. Similarly, U.S. Pat. No. 4,504,204, issued to Koga, discloses a pig train apparatus for use in low pressure distribution lines that employs a tether to guide the pigs into place and transfer resin from above ground tanks to the pigs. The resin is then injected through ports in the pigs. The injected resin, however, is intended to provide a seal rather than a structural repair. Last, U.S. Patent App. No. 2002/0083990, filed by Lundman, discloses a device having an inflatable bladder wrapped with a repair material such as a composite material impregnated with a curable resin. The device, which is tethered and pulled into place, is then inflated to force the repair material against the inner wall of the pipeline. The device, however, does not provide for remote repair or pressure isolation of the repair area, nor is it capable of providing multiple layers of composite material in a single deployment or subsequently moving downstream and applying a second repair.